10% Spring Hanger Variability
10% Spring Hanger Variability
(OP)
Dear piping engineers,
A question is raised in our company that why in stress analysis specs, spring hanger's variability is reduced from normal 25% to 10% for strain sensitive equipment?
The reason stated is that if the load on an equipment is within allowable limit, then what difference does it make if the variability of the spring is 10% or 20 plus %.
In my opinion, we want to restrict the variation of load on strain sensitive equipment (Pumps, turbines, compressors) as mechanically load may be acceptable and may not damage the nozzle, but the slight strain on it may misalign the shaft slightly which may reduce the bearing life. But counter argument is that for that reason allowable load is given, and piping load is maintained below that allowable so that no strain is transferred to bearings.
Am I right in this or there is some other reason? All help is appreciated.
A question is raised in our company that why in stress analysis specs, spring hanger's variability is reduced from normal 25% to 10% for strain sensitive equipment?
The reason stated is that if the load on an equipment is within allowable limit, then what difference does it make if the variability of the spring is 10% or 20 plus %.
In my opinion, we want to restrict the variation of load on strain sensitive equipment (Pumps, turbines, compressors) as mechanically load may be acceptable and may not damage the nozzle, but the slight strain on it may misalign the shaft slightly which may reduce the bearing life. But counter argument is that for that reason allowable load is given, and piping load is maintained below that allowable so that no strain is transferred to bearings.
Am I right in this or there is some other reason? All help is appreciated.





RE: 10% Spring Hanger Variability
RE: 10% Spring Hanger Variability
RE: 10% Spring Hanger Variability
@BigInch,
I agree that stress engineering is not an exact science. That is why in COADE Caesar II forum, John Breen once gave his opinion that a system failing with more than 100% stress ratio would not necessarily fail in actual and a system with less than 100% stress ratio is not necessarily safe.
Key is how accurately you can simulate the actual conditions.
RE: 10% Spring Hanger Variability
RE: 10% Spring Hanger Variability
Every word you wrote in your post is TRUE!
We have to be within reason and do our best within "available" time to come out with solution.
RE: 10% Spring Hanger Variability
Most systems fall down at the point someone has to build it and then all your analysis can be forgotten about.
BI deserves another star for that reply.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: 10% Spring Hanger Variability
RE: 10% Spring Hanger Variability
That's where experience comes in. Where I am now they think that allowing Utilisation factors up to 0.999 is acceptable because it is less than 1.00. When I say that they should be limiting the stress levels to around 80% of the Code they ask why since the Code allows up to 100%. I then tell them that the stress analysis they conduct is not "exact" due to tolerances and also the construction of the pipework will not be exact and the knuckle-rubbing gorillas on site fitting the pipe use turfors/winches or some other mechanical means to align the pipework thereby inducing prestress into the pipework which is not accounted for in the theoretical analysis they tend to start to understand a little.
RE: 10% Spring Hanger Variability